Bowling ball return and handling mechanism



April 23, 1963 J. ZUERCHER 3,036,776

BOWLING BALL RETURN AND HANDLING MECHANISM Filed Aug. 5, 1959 2 Sheets-Sheet 1 FIG.1 S

JOHN ZUERGHER m INEY April 23, 1963 J. ZUERCHER BOWLING BALL RETURN AND HANDLING MECHANISM Filed Aug. 5, 1959 2 Sheets-Sheet 2 .aw G F ma 3 v. m/ P M JOHN ZUERCHER ATTOR N EY United States Patent 3,086,776 BOWLING BALL RETURN AND HANDLING MECHANISM John Zuercher, Mansfield, Ohio, assiguor to American glachine & Foundry Company, a corporation of New ersey Filed Aug. 5, 1959, Ser. No. 831,846 Claims. (Cl. 273-49) This invention relates to bowling ball return and handling mechanism and more particularly to apparatus for effecting the removal of bowling balls from the pit of a bowling alley and delivering them to a return mechanism for return to a player at the head end of a bowling alley.

In the game of bowling, it is most desirable to remove a ball delivered into the pit of a bowling alley as rapidly as possible therefrom to a ball return device for return to the player at the head end of the alley. The rapid removal of the ball decreases the amount of elapsed time between successive deliveries of a ball by a player, thereby increasing the enjoyment of the game by the participants.

In many bowling establishments, it is customary to provide a common ball return for use with two adjacent bowling alleys, the ball return being located between the two alleys. With this type of arrangement, when balls are delivered from the pits of the alleys to the return runway, it is desirable to control the delivery of the balls in order that they will not be removed or delivered from both pits simultaneously and collide as they leave the pits.

The present invention is characterized by the provision of novel ball doors mounted in openings in the adjacent kickbacks of two side-by-side bowling alleys utilizing a common toggle connection for preventing the simultaneous exiting of balls from adjacent pits. Further, each door is provided with a novel ball-actuated latch mechanism for unlocking a door to permit the exit of a ball therethrough. This latch mechanism is provided with a freely rotatable locking element having a two-step locking action; the first step locks the door in partially open position when pins attempt to exit therethrough together with the ball, the second step releasing the door for complete opening when a ball only is exiting through the opening in the kickback.

It is therefore an object of the present invention to provide novel ball release apparatus for effecting the removal of bowling balls from the pit of a bowling alley.

It is likewise an object of the present invention to provide mechanism for removing bowling balls from the pits of two adjacent bowling alleys for delivery to a common ball return in which a toggle interlock ball door system is provided for preventing the simultaneous removal of bowling balls from the pits of the alleys to the mechanism.

A further object of the present invention is to provide an improved ball actuated latch mechanism for use with doors mounted in openings of the kickbacks in bowling alleys.

Another object of the present invention is to provide a ball actuated latch mechanism for use with doors mounted in openings of the kickbacks in bowling alleys operative to retain a door in partially opened position to prevent the exiting of pins together with a ball through the opening.

3,086,776 Patented Apr. 23, 1963 It is another object of this invention to provide an improved ball actuated latch mechanism for use with doors mounted in the openings of the kickbacks in adjacent bowling alleys, the latch mechanisms being positioned in their associated doors to effectively prevent a pin from opening a door, insuring against pin and ball interference as a ball exits through one of the openmgs.

Other objects and features of the invention will appear as the description of the particular physical embodiment selected to illustrate the invention progresses. In the accompanying drawings, which form a part of this specification, like characters of reference have been applied to corresponding parts throughout the several views which make up the drawings.

FIG. 1 is a partial side elevation illustrating a preferred embodiment of the invention as employed with two adjacent bowling alleys.

FIG. 2 is a plan view of the mechanism illustrated in FIG. 1.

FIG. 3 is a front view of a mechanism illustrated in FIGS. 1 and 2.

FIG. 4 is a view taken along line 4-4 of FIG. 3.

FIG. 5 is a view taken along line S5 of FIG. 3.

Referring to the drawings, the door mechanism is shown mounted between two adjacent alleys and arranged to deliver balls from the pits P1 and P2 of these alleys for automatic delivery to a ball return runway common to the two alleys. The ball lifting and return mechanism illustrated in the drawings is of the same general type as described and claimed in Patent 2,765,172 to Zuercher et al. for Bowling Ball Handling and Return Mechanism. If desired, other types of ball return mechanisms can be used.

Referring specifically to FIGURES l, 2 and 3, which show a preferred embodiment of the invention, each of the doors or gates, designated generally 10, is shown mounted in an opening 12 formed in adjacent kickbacks or side plates 14 of pits P1 and P2 of two side-by-side bowling alleys. Doors 10 are preferably concave to facilitate handling of balls. However, if desired, doors 10 could be flat without affecting the operation described hereinbelow. Each door 10 is supported on a bracket 16 which in turn is pivotally mounted on a vertical shaft 18. Shaft 18 is supported at its upper and lower extremities in bearing blocks 20, the lower bearing block 20 being supported on guide block 22 positioned in space S between side plates 14 as shown in FIGURES l, 2 and 3.

Each bracket 16 is provided with an arcuate extension 24 adjacent the upper portion thereof. Pivotally mounted in the free end of extension 24 is a vertical pivot pin 26. Pivotally mounted adjacent the upper end of pin 26 is one end of a link member 28. The free ends of each link member 28 associated with each door 10 are pivotally mounted in common together with one end of another link 31 on pin 32; thus forming a horizontal toggle joint. The other end of link 30 is secured to the upper end of a shaft 34 pivotally mounted in bracket 36 adjacent the mid-point thereof. Bracket 36, in turn, is mounted transversely in space S and secured at each end by brackets 38 to the inner face of each side plate 14.

To urge doors 10 into closed position in openings 12, each pin 26 associated with a door 10 is provided with 8. preferably U-shaped bracket 40 having a horizontal extension 42. The free end of each extension 42 supports one end of a tension spring 44, in the manner seen in FIGURE 3, which is operative to urge each door through pin 26 and bracket 16 into closed position in openings 12 in side plates 14.

To maintain doors 10 in closed position in openings 12, each door 10 is provided with a latching mechanism. This latching mechanism includes a bumper 46 mounted in an elongated arcuate slot 48 in door 10 with a portion thereof extending through slot 48 to the pit-side of door 10. Bumper 46 is mounted in the lower end of arm 50 which, is swingably mounted at its upper end on shaft 52 carried between a pair of downwardly depending arms 54. Arms 54 are preferably formed as an integral part of hub 56 which is rotatably supported on a horizontal shaft 58. Shaft 58 is supported at one end in a suitable bearing in the upper portion of its associated door 10. The other end of shaft 58 is supported in a suitable bearing in arm 60 formed preferably as an extension of bracket 16, as shown best in FIGURES 2 and 3.

In operation, a ball is delivered into pit P1 or P2 onto conveyor C1 and C2, moving continuously therein toward the rear thereof. A ball thus delivered is guided by back stops B and ball guide strips G, extending transversely beneath conveyors C1 and C2 laterally of its respective pit P1 and P2 toward its associated side plate 14. Balls delivered to side plate 14 are seated in a notch 62 formed in bounce boards 64 located beneath conveyors Cl and C2 adjacent ball doors 10. The continuous movement of conveyors C1 and C2 is operative to rotate a ball against door 10. A ball so rotating against door 10 frictionally engages bumper 46 which is formed preferably of a material having a high coefiicient of friction; such as rubber or other suitable material. Bumper 46 so engaged by a ball rotating thereagainst, is pivoted in the direction of arrow A (FIGURE 4). Such movement of bumper 46 in turn rotates arms 50 and 54 and hub 56.

However, during play if a bowling ball is delivered to door 10 at too great a speed to become properly seated in notch 62, such ball strikes bumper 46 which pivots about shaft 52, thus yielding with the ball and thereby preventing the ball from rebounding out of engagement therewith. Having thus dissipated the excess energy of the ball, spring 55 encircling an extension 53 of shaft 52 having one end 57 thereof bearing against an extension 51 of arm 50, is operative to return bumper 46 back into operative position in door 10. The other end 59 of spring 55 is positioned beneath a shoulder 61 formed in hub 56. Thus, spring 55 is operative to return bumper 46 to its operative position in door 10 and also assists in maintaining bumper 46 in frictional engagement with a ball delivered thereto.

Referring specifically now to FIGURES 4 and 5, hub 56 is provided at its upper end with a latch element 66, preferably formed integrally therewith, which, when door 10 has closed opening 12 is positioned adjacent the front or leading edge 63 of a pawl 68. Pawl 68 is rotatably mounted at one end on generally horizontal shaft 70, suitably supported at each end by a bracket 72 secured to the inner face of side plate 14 above opening 12. In addition, pawl 68 is provided with a transverse extension 74 which, when door 10 is in closed position and pawl 68 is in operative locking position with edge 63 adjacent element 66, bears against the top of one of the brackets 72 as shown in FIGURE 5. Extension 74 thus limits the downward rotation of pawl 68 about shaft 70.

As hub 56 is rotated as described hereinabove, latch member 66 is pivoted away from the leading edge 63 of pawl 68 thus permitting doors 10 to be swung under the weight of a ball bearing thereagainst inwardly in the direction of arrows B into space S (see FIGURE 2).

It will be understood that the latch mechanism detailed above greatly expedites ball removal from the pit of a bowling alley since a ball delivered to the ball door 10 4 can readily actuate latch element 66 by engaging bumper 46.

As a door 10 is thus rotated inwardly; for example, the lowermost door in FIGURE 2, extension 24 on bracket 16 is likewise pivoted inwardly as illustrated in FIGURE 2, to the position shown in dotted lines therein. This movement of extension 24 operates to urge the end of its associated link 28 in the direction of arrow C toward side plate 14. Such a movement of link 28 is operative to urge the other link 28 and link 30 in the direction of arrow D to the position illustrated in dotted lines in FIGURE 2. With one door 10 thus in open position, links 28 and 30 forming a horizontal toggle joint, in effect, move to an overcenter locked position, thereby preventing the opening of the other door 10 until the first door 10 has returned to a closed position, moving links 28 and 30 back into the position illustrated in full in FIGURE 2. Such an arrangement obviously prevents the simultaneous discharge of bowling balls from pits P1 and P2 into space S.

In addition, it will be understood that the movement of links 28 and 30 into overcenter position, operates to extend spring 44 which thereby assists in maintaining the second door 10 in closed position until the first door 10 has returned to closed position.

A ball thus actuating the latch mechanism to open door 10 is free to pass through opening 12 onto guide block 22 for delivery to rails R of ball elevating mechanism M, for return on a ball return track (not shown) to the head end of the alley.

As a ball disengages door 10 as it passes onto guide block 22 and rails R, door 10 is urged back into closed position in opening 12 by the action of spring 44 as described hereinabove. It will be understood that as a ball passes out of engagement with ball door 10, bumper 46, arm 50 and hub 56 pivot under their own weight back to generally a vertical position with bumper 46 resting against a rib 17 of bracket 16. In this position, as door 10 is pivoted back to closed position, latch element 66 en gages the underface of the inclined or cam section 69 of pawl 68, pivoting pawl 68 upwardly about shaft 70 thus permitting free passage of door 10 back to closed position. Pawl 68 then drops back to its original locking position shown in FIGURE 5 when latch member 66 is moved out of contact therewith as door 10 moves into opening 12.

Means is provided to prevent the exiting of a bowling pin through opening 12 together with a bowling ball. It is evident from the elevated position of bumper 46 in door 10 that only a ball can actuate the latch mechanism to effect the opening of door 10. However, as often happens, as door 10 is opened, as described hereinabove, a portion of a bowling pin lying in front of or in the way of a ball as it exits from the pit may precede the ball through opening 12. When this occurs, a wedging action occurs and such a bowling pin operates to urge the ball away from ball door 10, in order to exit first through opening 12. However, when a ball is thus moved out of engagement with bumper 46, bumper 46, hub 56 and latch element 66 attempt to return to the position illustrated in FIGURE 4 with bumper 46 adjacent rib 17. However, the latch mechanism is prevented from so returning since an edge of latch element 66 engages edge 67 of pawl 68. In this partially-rotated position, with edge 65 thereof in contact with edge 67 of pawl 68, lat-ch element 66 is engaged by shoulder 71 formed in pawl 68. The engagement of latch element 66 by shoulder 71 thus prevents further opening of door 10 in the direction of arrow B, FIGURE 2. Thus ball door 10 is retained in partially open position until the bowling pin attempting to exit through opening 12 has been move-d by its associated conveyor C1 or C2 around the bowling ball and back into its respective pit P1 or P2, thus substantially minimizing pin and ball interference at the ball exits. The bowling ball, now free to reengage bumper 46, pivots bumper 46 and latch element 66 to its fully-open position described hereinahove, moving edge 65 out of contact with edge 67 and urging latch member 66 away from shoulder 71. This permits ball door under the urging of a bowling ball to move to fully opened position allowing the ball to exit through opening 12 into space S for elevation by mechanism M to the ball return track (not shown) for return to a player at the head end of the alley.

It will be understood that the above described construction and operation has been limited to a single door in the interests of brevity. However, the construction and operation of the other door of a pair of side-by-side installations is of like construction and operates in like manner.

What I claim is:

1. Bowling ball handling and return apparatus for use with a bowling alley having a pit at one end, and kickbacks at opposite sides of said pit, one of said kickbacks being provided with a ball opening through which balls roll out of said pit, said apparatus comprising a door, supports mounting said door for movement into and out of closed position in said opening, means normally urging said door into closed position in said opening, lock means for said door normally securing said door in closed position in said opening, said lock means including a two-position locking element, ball-actuated unlocking means carried by said door for effecting the release of said door for movement of a ball through said opening, said lock means and said unlocking means coacting to relock said door in partially opened position at a second locking position of said locking element in the event a bowling pin attempts to exit with a ball through said opening.

2. Bowling ball handling and return apparatus for use with two adjacent bowling alleys, each of said alleys having a kickback at one end of said alley provided with a ball opening and a ball return device located between said kickbacks and adapted to receive balls passing through said openings, said apparatus comprising a door for each of said kickbacks, means mounting each of said doors for movement into and out of closed position in said openings and into and out of open position be tween said kickbacks, means normally urging said doors into closed position in said openings, lock means for each of said doors normally securing each of said doors in operative position closing said openings, ballactuated unlocking means operatively associated with each of said doors for effecting the opening of said doors for movement of a ball from one of the pits therepast and through its associated opening corresponding to one of said doors and toggle means including a toggle joint and operating elements connected to each of said doors and operative in response to the opening of one of said doors to lock said toggle joint, said toggle means thereby maintaining the other of said doors in closed position to prevent simultaneous exiting of balls from said pits.

3. Bowling ball handling and return apparatus for use with two adjacent bowling alleys, each of said alleys having a kickback at one end of said alley provided with a ball opening and a return device located between said kickbacks and adapted to receive balls passing through said openings, said apparatus comprising a door for each of said kickbacks, means mounting each of said doors for movement into and out of closed position in said openings and into and out of open position between said kickbacks, means normally urging said doors into closed position in said openings, lock means for each of said doors normally securing each of said doors in operative position closing said openings, ball-actuated unlocking means operatively associated with each of said doors for effecting the opening of said doors for movement of a ball from one of the pits therepast and through its associated opening corresponding to one of said doors, means connected to each of said doors and actuated by the opening of one of said doors for maintaining the other of said doors in closed position until said opened door is returned to closed position, whereby simultaneous exiting of balls from each of said pits is prevented, said lock means including a two-position locking element operative to relock its associated door in partially opened position at a second locking position of said locking element to prevent the exiting of a pin through said opening associated with said door.

4. Bowling ball handling and return apparatus for use with two adjacent bowling alleys, each of said alleys having a kickback at one end of said alley provided with a ball opening and a ball return device located between said kickbacks and adapted to receive balls passing through said openings, said apparatus comprising a door for each of said kickbacks, means mounting each of said doors for movement into and out of open position between said kickbacks, means normally urging said doors into closed position in said openings, lock means for each of said doors normally securing each of said doors in operative position closing said openings, ball-actuated unlocking means operatively associated with each of said doors for effecting the opening of said doors for movement of a ball from one of the pits therepast and through its associated opening corresponding to one of said doors, a link pivotally connected to each of said doors, an arm, means swingably mounting said arm in the space between said kickbacks, means pivotally connecting in common the free ends of said links and said arm forming a toggle joint whereby as one of said doors is moved toward open position said links and said arm coact to maintain the other of said doors in closed position until said open door is returned to closed position, thereby preventing simultaneous exiting of balls from each of said pits to said return device, said lock means including a pawl, means mounting said pawl adjacent said door, a latch element positioned on said door and adjacent a portion of said pawl to maintain said door in locked position, said ball actuated unlocking means including a ball-engaging member, a shaft rotatably mounting said member in said door with a portion of said member extending into said pit, means for directing a ball in said pit into rotary engagement with said member to rotate said member about said shaft, means connecting said ball engaging member to said latch eiement whereby, as said ballengaging member is rotated about said shaft, said latch element is moved out of position adjacent said pawl to effect the unlocking of said door, said pawl having a second locking portion, said ball-engaging member being operative to return said latch element toward locking position, when a ball has been moved out of rotary engagement with said ball-engaging member by a bowling pin attempting to exit through said opening, said latch element upon return toward locking position engaging said second locking portion of said pawl to maintain its associated door in partially open position to prevent the exiting of said pin through said opening.

5. Bowling ball handling and return apparatus for use with a bowling alley having a pit at one end, kickbacks at opposite sides of said pit, one of said kickbacks being provided with a ball opening through which balls roll out of said pit, said apparatus comprising a door, supports mounting said door for movement into and out of closed position in said opening, means normally urging said door in closed position in said opening, a pawl, means mounting said pawl adjacent said door, a latch element positioned on said door and adjacent a portion of said pawl to normally maintain said door in closed position in said opening, a ball engaging member, a shaft rotatably mounting said member in said door with a portion of said member extending into said pit, means for directing a ball in said pit into rotary engagement with said member to rotate said member about said shaft, means connecting said ball engaging member to said latch element whereby as said ball engaging member is rotated about said shaft, said latch element is moved out of position adjacent said pawl to efi'ect the unlocking of said door, said pawl having a second locking portion, and said ball-engaging member being operative to return said latch element toward locking position, when a ball has been moved out of rotary engagement with said ball-engaging member by a bowling pin attempting to exit through said opening, said latch element upon return toward locking position engaging said second locking portion of said pawl to maintain its associated door in partially open position to prevent the exiting of said pin through said opening.

6. In a bowling ball handling and return apparatus for use with two adjacent bowling alleys each having a kickback disposed at the pit end of the alley and provided with a ball opening, the kickbacks being spaced apart with their ball openings opposed laterally across the space between the kickbacks so that balls can be delivered from both alleys to the space between the kickbacks for return to the players end of the alleys, the combination of a door for each of said openings; means mounting each of said doors in operative relation with a different one of said openings for pivotal movement between a first position in which the door closes the opening with which it is associated and a second position in which the door is displaced from the opening into the space between the kickbacks, the pivotal axes of said doors being parallel; a pair of rigid extensions of equal length each connected to a different one of said doors and projecting into the space between the kickbacks; an arm disposed between the kickbacks, said arm being pivoted at one end to a fixed support; a pair of links of equal length pivoted together and to the other end of said arm at one end and each pivotally connected at its other end to a different one of said extensions, all of the pivotal axes for said arm and said links being parallel to the pivotal axes of said doors; spring means connected between said extensions and resiliently biasing said doors to their closed positions, said extensions, links and arm coacting to form a toggle joint which is pivoted to locked condition when either of said doors is pivoted to open position whereby when one of said doors is opened, the resultant locking of the toggle joint prevents the other door from being opened; lock means operatively associated with each of said doors and normally securing the doors in their closed positions; and ball-actuated means operatively associated with each of said doors for unlocking the same.

7. Bowling ball handling and return apparatus for use with a. bowling alley having a pit at one end and kickbacks at opposite sides of said pit, one of said kickbacks having a ball opening through which a ball can roll out of said pit, said apparatus comprising a door, means mounting said door for movement into and out of closed position in said opening, means normally urging said door toward said closed position, and locking means for said door comprising: a pawl mounted adjacent said door, a latch on said door having a normal position adjacently opposite said pawl to maintain the door in closed position, means mounting said latch for movement out of the range of engagement with said pawl to permit opening of the door, said pawl having an intermediate step permitting partial door opening, means on said door extending therebeyond into the pit area and operable by engagement with a notating ball to move said latch from said normal po sition and completely out of the range of engagement with said pawl, said means also permitting said latch to return to a position adjacently opposite the intermediate step of the pawl to relock the door in a partially open position upon interference with the exit of a ball by a pin attempting to exit through the door.

8. Bowling ball handling and return apparatus for use with a bowling alley having a pit at one end, kickbacks at opposite sides of Said pit, one of said kickbacks being provided with a ball opening through which balls roll out of said pit, said apparatus comprising a door, supports mounting said door for movement into and out of closed position in said opening, means normally urging said door in closed position in said opening, a pawl, means mounting said pawl adjacent said door, a latch element positioned on said door and adjacent a portion of said pawl to normally maintain said door in closed position in said opening, a ball engaging member, shaft means mounting said member for respective movements both in a first plane substantially perpendicular to the door, with a portion of said member extending into the pit, whereby said member is operative to dissipate excess energy of a ball delivered thereto while maintaining the ball in frictional engagement therewith, means for directing a ball in said pit into rotary engagement with said member to rotate the same within said first plane, and means connecting said latch to said member whereby, as said member is rotated in said first plane, said latch is moved out of position adjacent said pawl to etfect unlocking of said door.

9. In a bowling alley installation having a kickback disposed between the pit of the alley and a space to which bowling balls are to be delivered for return to the players end of the alley, the kickback being provided with a ball opening, the combination of a door operatively arranged with respect to the opening in the kickback for movement between a position in which said door closes the opening and a position in which the door allows a ball to pass through the opening; ball delivery means arranged in the pit and operative to deliver balls into proximity with said door, when said door is closed, with each ball so delivered rotating in a predetermined direction relative to said door; means biasing said door to closed position with respect to the opening; latch means for retaining said door in closed position, said latch means comprising a fixed member disposed adjacent the opening and a movable member mounted on said door for actuation from a latched position, in which the same is normally engaged with said fixed member, to an unlatched position; and a ball-engaging member mounted on said door for pivotal movement about a first axis at least generally parallel to the plane of the door and also about a second axis at least generally at a right angle to the first axis, said ball-engaging member being thereby movable from a first, normal position, in which it projects into the path of travel of balls delivered into proximity with said door by said ball delivery means when said door is closed, to a second position displaced from said first position in a direction corresponding to the predetermined rotation of balls so delivered, said ball-engaging member and said movable member of said latch means being interconnected and movement imparted to said ball-engaging member by a ball delivered by said ball delivery means serving to actuate said movable member of said latch means to its unlatched position.

10. In a bowling alley installation having a kickback disposed between the pit of the alley and a space to which bowling balls are to be delivered for return to the player's end of the alley, the kickback being provided with a ball opening, the combination of a door operatively arranged with respect to the opening in the kicback for movement between a position in which said door closes the opening and a position in which the door allows a ball to pass through the opening; ball delivery means arranged in the pit and operative to deliver balls into proximity with said door, when said door is closed, with each ball so delivered rotating in a predetermined direction relative to said door; means biasing said door to closed position with respect to the opening; latch means for retaining said door in closed position, said latch means comprising a fixed member disposed adjacent the opening and a movable member mounted on said door for actuation from a latched position, in which the same is normally engaged with said fixed member, to an unlatched position, a hub disposed at the top of the door and projecting away from the pit of the alley, said hub being arranged to pivot about a horizontal axis, a ball engaging member mounted on said hub for pivotal movement about an axis at a right angle to the pivotal axis of said hub, said door being provided with an opening and said ball-engaging member having a portion projecting through said opening for engagement with a hall approaching the door, said ballengaging member thereby being movable about said first mentioned horizontal axis from a first, normal position, in which it projects into the path of travel of balls delivered into proximity with said door by said ball delivery means when said door is closed, to a second position displaced from said first position in a direction corresponding to the predetermined rotation of balls so delivered, said ball-engaging member and said movable member of said latch means being interconnected and movement imparted to said ball-engaging member by a ball delivered by said ball delivery means serving to actuate said movable member of said latch means to its unlatched position.

References Cited in the file of this patent UNITED STATES PATENTS Keesling Ian. 18, 1955 Zuercher et al. Oct. 2 1956 

1. BOWLING BALL HANDLING AND RETURN APPARATUS FOR USE WITH A BOWLING ALLEY HAVING A PIT AT ONE END, AND KICKBACKS AT OPPOSITE SIDES OF SAID PIT, ONE OF SAID KICKBACKS BEING PROVIDED WITH A BALL OPENING THROUGH WHICH BALLS ROLL OUT OF SAID PIT, SAID APPARATUS COMPRISING A DOOR, SUPPORTS MOUNTING SAID DOOR FOR MOVEMENT INTO AND OUT OF CLOSED POSITION IN SAID OPENING, MEANS NORMALLY URGING SAID DOOR INTO CLOSED POSITION IN SAID OPENING, LOCK MEANS FOR SAID DOOR NORMALLY SECURING SAID DOOR IN CLOSED POSITION IN SAID OPENING, SAID LOCK MEANS INCLUD- 